This indicates an attack attempt to exploit a Denial of Service vulnerability in Kerberos.
The vulnerability is due to an NULL pointer dereference error when vulnerable module handles a crafted TGS request. A remote attacker may be able to exploit this to cause a denial of service condition on the affected system.
MIT Kerberos 1.11.3 and prior
Denial of Service: Remote attackers can crash vulnerable systems or services
Apply the most recent upgrade or patch from the vendor.